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SB-200

Y

YardDog

WDX-128 N/W Arkansas
Jan 29, 2021
160
421
73
N/W Arkansas
I just acquired a beautiful sb-200. It's super clean inside and out, and was in use until the previous owner became a silent key. I'd like to pair an ic-7300 with it but want to be sure they play nice. From what I've found on the interweb, I'll need to set the transmit delay to 25mS and I was given an Ameritron arb-704 to use as a buffer. Is there anything else I need before I can safely take it for a test drive? Tuning up a tube amp is no big deal but I've never used a heathkit before and don't want to screw up the amp or the radio. Thanks in advance
WDX-128
 

YardDog said:
I just acquired a beautiful sb-200. It's super clean inside and out, and was in use until the previous owner became a silent key. I'd like to pair an ic-7300 with it but want to be sure they play nice. From what I've found on the interweb, I'll need to set the transmit delay to 25mS and I was given an Ameritron arb-704 to use as a buffer. Is there anything else I need before I can safely take it for a test drive? Tuning up a tube amp is no big deal but I've never used a heathkit before and don't want to screw up the amp or the radio. Thanks in advance
WDX-128
Click to expand...
The only real concern, is that you need a relay buffer, between the radio and send of the amp, due to the fact that the T/R relay in the amp, uses a 120 volt coil.
 
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SuperLid said:
uses a 120 volt coil
Click to expand...
And there's a bonus. The voltage on the amplifier's keying jack is negative. No choice here but to insert a buffer box containing a relay between this model and the radio.

Years ago, a customer brought in a Yaesu FT757 that had the linear-keying out put fried. Literally, didn't burn foil traces, but a string of parts connected to the linear key jack were failed short internally. This radio tolerates up to about 16 Volts POSITIVE DC volts from the linear, and uses a transistor that closes the linear's relay circuit to ground.

The National NCL-2000 amplifier he hooked to the radio uses 12 Volts AC for the relays. The negative side of the AC created a reverse-polarity condition in the radio, and fried things, the way reverse polarity will do to transistors.

Old amplifiers were intended to use with radios that had a proper relay inside them for this purpose. And if the radio is too new to have that relay, it has to be provided in its own box.

73
 
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YardDog said:
Now I'm scratching my head. I thought the 704 was the relay buffer. Do I even need the 704? What relay buffer do you recommend? Sorry to be so ignorant, but coupling modern radios to antique amps is uncharted waters for me.
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Not really....you just need a relay, a 12V source to energize the coil, using the radio PTT/SEND key line to ground the coil. Use the N.O. contact between ground and the relay in jack of the amp. There is also the solid state approach you could take as well, in lieu of a relay.
 
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SuperLid said:
There is also the solid state approach you could take as well, in lieu of a relay
Click to expand...
I wish someone would sell a buffer box that uses a transistor with a full-wave bridge rectifier to resolve polarity issues. This would take the place of a relay for AC or either polarity of DC. Any component with moving parts inside it will wear out eventually.

The ARB704 is a plug-and-play solution, no soldering iron required.

And if you fancy rolling your own, that would be cool, too.

73
 
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Finally got around to firing it up today. Had to make up a cord for the rf into the amp, but it's working fine. I'm putting 45w in and getting 425w out on 11m ssb. More than I expected on that band, no idea what it will do on 40m or 80m. But I'm happy with the output, especially since I'm only in it for $150.
 
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